Falls from a height generally result in axial loading of the spine, which may result in a “burst” fracture or wedge compression fracture, depending on the degree of flexion of the trunk at the time of impact. These fracture patterns are possible with any mechanism associated with axial compression and can occur with motor vehicle accidents and sporting injuries.16 Compression of the vertebra with the trunk flexed creates the greatest forces in the anterior aspect of the vertebra, leading more commonly to anterior column wedging. This is in contrast to the trunk in an extended position, which loads the vertebral body more symmetrically. Fractures in this case often collapse with radial expansion or “bursting.” Displacement of the posterior vertebral body fragments into the spinal canal may cause injury or compression of the neurologic elements (spinal cord or cauda equina).34
If the magnitude of injury sustained seems out of proportion to the force applied, the possibility of an insufficiency fracture due to weak bone should be considered. Osteoporotic insufficiency fractures, common in the elderly, are rare in children; however, several disease states may predispose children to these fractures. Chronic corticosteroid use associated with the management of many pediatric rheumatologic and cancerous diseases often leads to osteoporosis and increased risk of compression fractures.80 In addition, primary lesions of the bone, such as Langerhans histiocytosis, often affects thoracic vertebrae.4,25 Other tumors and infections warrant consideration when nontraumatic compression fractures are identified.54,67
Associated Injuries with Thoracolumbar Spine Fractures
Just as the mechanism of injury should raise suspicion of a particular injury (e.g., lap belt injury and flexion–distraction lumbar fracture pattern), so should the presence of one injury raise suspicion of a concomitant associated injury. First, any spinal fracture should be considered a significant risk factor for a spinal fracture at another level.50 The traumatic force required to create one fracture is often enough to result in one or more additional fractures at other locations. Similarly, a cervical injury is frequently associated with closed head injury and vice versa.
The lap belt mechanism of injury is well known to create flexion–distraction injuries of the spine, but also is associated with intra-abdominal injury.65 Compressed between the seat belt and the spinal column, the aorta, intestinal viscera, and abdominal wall musculature are at risk for laceration. Abdominal injuries are present in almost 50% of pediatric patients with Chance fractures.56 Ecchymosis on the anterior abdomen is suggestive of intra-abdominal injury that warrants further evaluation with laparoscopy, laparotomy, or additional imaging by computed tomography (CT).5,76 A high index of suspicion is required, because missed injuries may be life-threatening.47
Associated injury to the spinal cord has obvious significance and may be present with many fracture patterns. Disruption of the stability of the spinal column or bony intrusion into the spinal canal may result in compromise of neurologic function. All patients with a known spinal column fracture or dislocation warrant a careful neurologic examination. Overall, most pediatric patients with thoracolumbar fractures are neurologically intact (85%), and less commonly present with SCIs (incomplete in 5% and complete in 10%).20 Similarly, patients with a traumatic neurologic deficit require a careful evaluation of the spinal column integrity. There are, however, a subset of patients who present with SCI without radiographic abnormality.57,58 This scenario has been termed SCIWORA, a phenomenon much more common in children than adults. It is thought that the flexibility of the immature spine allows spinal column segmental displacements great enough to lead to SCI without mechanically disrupting the bony and/or ligamentous elements.57 Although these injuries may not be visible on plain radiographs, nearly all will have some evidence of soft tissue injury of the spine on more sensitive magnetic resonance imaging (MRI) studies.29 The term SCIWORA is less relevant in the era of routine MRI, which is now obtained in all patients with possible SCI39 and some have suggested a new acronym SCIWONA (SCI without neuroimaging abnormality).79,90
Signs and Symptoms of Thoracolumbar Spine Fractures
Careful evaluation of a patient with a potential traumatic spinal injury begins as with any serious trauma victim. The ABCs of resuscitation (airway, breathing, circulation) are performed while maintaining cervical and thoracolumbar spinal precautions. The frequency of spinal injuries in the setting of major trauma (motor vehicle accident, fall, etc.) is particularly high. After stabilizing the cardiorespiratory systems, symptoms of pain, numbness, and tingling should be sought if the patient is old enough and alert enough to cooperate. Pain in the back is often not appreciated when other distracting injuries exist and the patient is immobilized on a backboard. Examination of the back must not be forgotten and is performed by logrolling the patient. Visual inspection, along with palpation, should seek areas of swelling, deformity, ecchymosis, and/or tenderness that may provide a clue to the presence of an injury. In trauma patients, thoracolumbar fractures are more common in older children and adolescents, and there is a low mortality rate and infrequent need for operative stabilization.71 Clinically the ability to diagnosis a thoracolumbar spine fracture in pediatric trauma patients has been demonstrated to have good sensitivity and average specificity.37 Hence routine screening radiographs of any patients suspected of having a thoracolumbar spine injury should be performed, to minimize the likelihood of missing an injury.
Neurologic examination provides information on the integrity of the spinal cord. The age of the patient may limit the thoroughness of this assessment, but some indication of sensory and motor function should be sought. In cases of spinal cord deficit, a detailed examination of the strength of each muscle group, sensory levels, and rectal tone will need to be serially compared over time and the quality of the documentation cannot be overemphasized. The prognosis for recovery is significantly better if the SCI is incomplete.13,32,83 The status of the neurologic function over time may lead to important treatment decisions regarding the necessity and timing of surgical intervention. A progressive neurologic deficit warrants immediate surgical attention, whereas an improving status may suggest a less urgent approach. Overall, the physical examination has a sensitivity of 87% in identifying thoracolumbar fractures.71
Imaging and Other Diagnostic Studies for Thoracolumbar Spine Fractures
Following a careful clinical examination of all patients with a suspected spinal injury, plain radiographs are usually valuable. An alert, cooperative patient without pain or tenderness in the back can be cleared without radiographs. However, any patient with a significant mechanism or associated injury (motor vehicle accident, fall from greater than 10 ft, major long-bone fracture, cervical or head injury) requires thoracolumbar spine radiographs if they have spinal tenderness, are obtunded, or have a distracting injury. Initial films should include supine anteroposterior (AP) and lateral views of the thoracic and lumbar spine. In addition, because of the strong association between cervical spine fractures and thoracolumbar spine fractures after blunt vehicular trauma, routine imaging of the complete spine when a cervical fracture is identified is indicated.87
Plain radiographs often show relatively subtle findings that should be sought in all cases. On AP radiographs, soft tissue shadows may be widened by paravertebral hematoma. The bony anatomy is viewed to evaluate for loss of height of the vertebral body as compared with adjacent levels. Similar comparisons can be made with regard to interpedicular distance and interspinous spacing.10 Lateral radiographs give important information about the sagittal plane: Anterior vertebral wedging or collapse or posterior element distraction or fracture. Careful scrutiny of the plain radiographs is always prudent; however, the CT scan will nearly always be used to clarify any suspected fractures. Antevil et al.1 reported the sensitivity of plain radiographs to be 70% (14 of 20 patients) for spine trauma, whereas the sensitivity was 100% for CT scanning (34 of 34 patients).
CT is now a standard component of the evaluation of many trauma patients. Multidetector scanners allow rapid assessment with axial, coronal, and sagittal images for patients with plain radiographic abnormalities. The axial images are best for evaluating the integrity of the spinal canal in cases of a burst fracture, whereas the sagittal views will demonstrate vertebral body compression as well as posterior element distraction or fracture. In addition, major dislocations easily seen on plain radiographs will be better understood with regard to the space left in the spinal canal for the neurologic elements. The amount of spinal canal compromise has been correlated with the probability of neurologic deficit.55
MRI is the modality of choice for evaluating the discs, spinal cord, and posterior ligamentous structures.39,46,77 Although more difficult to obtain in a multiply injured patient, this study is mandatory in patients with a neurologic deficit to assess the potential cause of cord dysfunction. The MRI is able to distinguish areas of spinal cord hemorrhage and edema. Assessment of the posterior ligamentous complex (PLC) is critical in differentiating stable and unstable burst fractures, as well as compression fractures and flexion–distraction injuries. Although subject to overinterpretation, MRI has been shown to modify the diagnosis made by plain radiographs and CT and correlates very well with intraoperative findings of the structural integrity of the posterior soft tissues.46,62
Classification of Thoracolumbar Spine Fractures
There are several methods of classifying thoracolumbar fractures: Holdsworth—two column, Denis—three column,17 McCormack—load sharing,53 Gertzbein—comprehensive,27 Thoracolumbar Injury Classification and Severity Score,61 each with purported advantages. Designed primarily with the adult spine fracture patterns in mind, the Denis classification translates well for the categorization of most pediatric thoracolumbar injuries.44 Based on theories of stability related to the three-column biomechanical concept of the spine (anterior, middle, posterior columns), the Denis classification in its simplest form includes compression, burst, flexion–distraction, and fracture-dislocations (Fig. 24-2).
Compression fractures are the most common thoracolumbar spine fracture pattern.11,35 The vertebral body loses height anteriorly compared with the posterior wall. The anterior aspect of the vertebral body is involved, but the posterior wall of the vertebral body is by definition intact. Axial load with flexion is the common mechanism. Depending on the degree and direction of flexion, the wedging may vary between the coronal and sagittal planes (Fig. 24-3). The percentage of lost height defines the severity of compression fractures, which rarely have an associated neurologic deficit. However, the fractures are often associated with similar or occasionally more severe fractures at adjacent or distant levels. Contiguous compression fractures, each of a modest degree, together may result in a substantial kyphotic deformity. Because the cause of these injuries, such as a fall, is fairly common, it is at times necessary to determine if a wedged vertebra seen radiographically represents an acute compression fracture, sequelae of Scheuermann kyphosis, or a remote injury. Clinical examination can localize pain to the site of the fracture in acute injuries; however, MRI or bone scanning can confirm acute fracture based on signal changes and increased isotope uptake.
Burst fractures likely represent a more severe form of compression fracture that extends posteriorly in the vertebral body to include the posterior wall (middle column). Axial compression is the primary mechanism, although posterior ligamentous injury and/or posterior element fractures may also occur. Laminar fractures have been known to entrap the dural contents. The fractures are most common in the lower thoracic and upper lumbar levels. Associated neurologic injury is related to the severity of injury (greater injury index scores correlate with greater frequency of SCI49) and the degree of spinal canal encroachment by retropulsed bony fragments.34 SCI at the thoracolumbar junction may result in conus medullaris syndrome or cauda equina syndrome. Careful examination of the perineal area is required to identify these spinal lesions.
Flexion–distraction injuries are especially relevant to the pediatric population because this classic lap belt injury is more frequent in backseat passengers, particularly when a shoulder strap is lacking. Motor vehicle accidents are the primary cause of this injury. The lap belt, which restrains the pelvis in adults, may ride up onto the abdomen in children. Chance, and later Smith, described how with a frontal impact, the weight of the torso is driven forward, flexing over the restraining belt. With the axis of rotation in front of the spine, distractive forces are placed on the posterior elements, with variable degrees of anterior vertebral compression. This three-column injury is generally unstable. The disruption of the posterior elements may occur entirely through the bony (Chance) or ligamentous (Smith) elements, although many times the fracture propagates through both soft and hard tissues.
The injury is most obvious on lateral radiographs; however, if no fracture exists, widening of the intraspinous distance may be the only finding on an AP radiograph. Standard transverse plain CT imaging may also miss this injury because the plane of injury lies within the plane of imaging. One classic finding in ligamentous flexion–distraction injuries is the “empty facet” sign. When the inferior articular process of the superior vertebra is no longer in contact with the superior articular process of the inferior vertebra, the facet appears empty in the transverse CT image.26 Sagittal reconstructions are most revealing and MRI will provide information about the integrity of the PLC. Identification of a purely intravertebral flexion–distraction fracture is important, because this may alter the treatment in patients with these injuries compared to those with severe ligamentous injury.
Fracture-dislocations of the spinal column result from complex severe loading mechanisms. These are by definition unstable injuries with a component of shearing and/or rotational displacement. A special note in the pediatric population is the documentation of this injury pattern in young patients exposed to nonaccidental trauma.18,42
Injury patterns specific to the pediatric population that do not fit the Denis classification include apophyseal avulsion fractures and SCIWORA. Apophyseal injuries, typically of the lumbar spine, occur in adolescents as a result of trauma. The mechanism is thought to be related to flexion with a portion of the posterior corner of the vertebral body (ring apophysis) fracturing and displacing posteriorly into the spinal canal. Symptoms may mimic disc herniation, although the offending structure is bone and cartilage rather than disc material (Fig. 24-4).19,21
The concept of SCIWORA was popularized by Pang and Wilberger58 who described their experience at the University of Pittsburgh. They noted a series of patients presenting with traumatic SCIs that were not evident on plain radiographs or tomograms. Several mechanisms to explain these findings have been proposed, including spinal cord stretch and vascular disruption/infarction. MRI studies have confirmed patterns of both cord edema and hemorrhage in such cases.29 Important additional facts about SCIWORA include the finding that some patients had a delayed onset of their neurologic deficits. Transient neurologic symptoms were persistent in many who later developed a lasting deficit. In addition, the younger patients (less than 8 years old) had more severe neurologic involvement.7,57,58
Outcome Measures for Thoracolumbar Spine Fractures
SCIs in children have remarkable potential for recovery. In a study from a major metropolitan trauma center, complete SCIs were associated with fatal injuries in one-third and no neurologic recovery in another third, whereas most of the remaining one-third of patients made improvements that ultimately allowed functional ambulation. Less surprisingly, nearly all patients with incomplete SCI made some improvement over time as well.83 This ability to recover, even from complete injuries, has led some to suggest more aggressive attempts at spinal cord decompression in the early course of treatment,23,59 whereas others have suggested a period of “spinal cord rest” with observation.49 In adults, early fracture fixation has been shown to be beneficial, minimizing respiratory morbidity and decreasing days in the intensive care setting and length of hospital stay.6 There is certainly no controlled series of pediatric patients treated by both approaches to support either hypothesis. The data do, however, suggest a more optimistic view regarding the potential recovery of traumatic SCIs in children compared with adults.
Spinal column structural integrity should be assessed in all cases of injury because the functional capacity of the vertebral elements to protect the spinal cord will continue to be required. This evaluation may be performed with functional radiographs, such as flexion–extension views (much more common in the cervical spine) or with an MRI evaluation of associated soft tissue injuries that may coexist with more obvious bony fractures. Several methods of estimating spinal column stability have been proposed including the three-column concept of Denis.17 Based on division into anterior, middle, and posterior columns, injuries to two and certainly three of these sagittal columns may be associated with an unstable injury pattern. Plain radiography with a CT scan is appropriate for evaluating the bony elements. An MRI is often required to elucidate the nature of the disc and ligamentous injuries.30,39,78 MRI is extremely sensitive and, given the brightness of edema fluid on T2 images, may be overinterpreted. A study correlating MRI and intraoperative surgical findings, however, demonstrated high levels of both sensitivity and specificity in the MRI evaluation of posterior soft tissue injuries (Fig. 24-5).46
The ultimate treatment goal is a stable spinal column. This often requires surgical treatment in unstable fracture patterns. In contrast, most stable injuries can be managed nonoperatively. There are particular exceptions to these generalizations, of course. At times the associated SCI or a substantial associated deformity may alter the treatment approach to an otherwise mechanically stable injury. The presence of a complete SCI in a child younger than 10 years is also a determinant that may affect treatment strategies. The incidence of paralytic spinal deformity (scoliosis) is nearly 100% in such cases, and a long instrumented fusion will likely be required at some point.45,60 Depending on the fracture pattern and age of the patient, it may be prudent to include much of the thoracic and lumbar spine in the initial instrumented fusion.52 However, in the patient without neurologic deficit, there is evidence that the use of posterior stabilization of thoracolumbar fractures using nonfusion methods followed by removal of metal implants within an appropriate period appears to be a safe, viable option.41
PATHOANATOMY AND APPLIED ANATOMY RELATING TO THORACOLUMBAR SPINE FRACTURES
The thoracic and lumbar spine links the upper and lower extremities through the torso. The 12 thoracic and 5 lumbar vertebrae are joined by intravertebral discs and strong ligaments, both anteriorly and posteriorly. The bony architecture of the vertebrae varies, with the smaller thoracic vertebrae having a more shingled overlapping configuration compared to the lumbar segments. The thoracic facets are oriented in the coronal plane whereas those in the lumbar spine lie nearly in the sagittal plane (Fig. 24-6).